Portable lawn care implements having an elongated boom and an internal combustion engine or electric motor at the user's end of the boom require an angle gear drive for transferring rotary movement of an input shaft to the output shaft. The output shaft drives a cutting tool or work engaging member, such as a line trimmer, pruning blade, edger or cultivator which is normally rotated about an axis obliquely angled relative to the axis of the elongated boom. To assure customer satisfaction, angled gear drives should be ruggedly designed for durability. Angled gear drives are a significant cost item in the manufacture of portable lawn care implements.
One example of a gear box for a grass trimmer is disclosed in U.S. Pat. No. 4,507,865 to Inaga et al. Each half of the gear box housing is shaped from stamped steel sheet. The halves are locked together by folding back flanges which are formed on the two gear box halves. Input and output gears are fixed to shafts and meshed within the gear box. Screws retain the gears in the gear box. A grease cup is provided on one side of the gear box.
Another example of a grass trimmer gear case is disclosed in U.S. Pat. No. 5,103,561 to Harada et al. In this design, bevel gears of an input shaft engage an output shaft through sealless ball bearings which are axially press fitted and retained in the gear case by on-shaft retainer rings. The retainer rings are fitted in annular grooves formed on the respective input and output shafts. The gear case is understood to be a one piece gear case.